I do use my iPod (20 GB, 4G) quite a bit, often with a Griffin RoadTrip that I won in a
TUAW contest. (Linked because I think they're good, not because I won the contest.)
Besides that, I also find myself frequently using my iBook. I sometimes couple it up with an Griffin AirClick USB (also won in the contest) that lets me control iTunes without having to be right there. Quite handy if you just got out of the shower and want some muzak.